1. Field of the Invention
The present invention pertains to balloon catheters which are useful in performing pulmonary artery catheterization and more particularly to disposable multi-lumen balloon catheters containing an axial facing pressure transducer which are capable of reproducably and accurately measuring intravascular and intracardiac pressure precisely as well as being capable of being used for thermodilution studies.
2. Description of the Prior Art
Typically, balloon catheters such as the Swan-Ganz thermodilution catheter have been used to obtain certain important cardiac diagnostic information. A single catheter insertion could be used for measuring pulmonary artery and pulmonary capillary wedge pressures, right atrial pressure as well as sampling from either the right atrium or pulmonary artery, as well as injection of a cold bolus solution and detection of temperature change for a determination of cardiac output. In one example of such a catheter which has been widely used, a quadruple lumen seven french catheter body with a balloon at the distal end was structured with a large lumen terminating at the tip of the catheter. This lumen was employed for obtaining pulmonary artery pressure or pulmonary capillary wedge pressure using a fluid coupling. Another lumen terminated in an injection orifice approximately 30 cm proximal to the distal tip of the catheter which provided for injection of cold solution into the right atrium or superior vena cava when the catheter tip was positioned in the pulmonary artery. Central venous pressure could also be measured through this lumen as an alternative to injecting a cold solution. Another lumen was provided for gaseous balloon inflation and the last lumen was provided to carry the electrical leads to the thermistor temperature detector which was exposed at the surface of the catheter about 3.5 cm proximal to the tip.
The direct method of measuring blood pressure provided by the Swan-Ganz catheter employed a hydraulic coupling system which exhibited several disadvantages in use. The principal disadvantage has been termed overshoot since the fluid coupling tended to produce a lag in the measurement which could mask or obscure valuable information and, in some situations, could produce a pressure reading that gave a false indication of a functional condition.
Likewise, movement of the catheter would produce variations in readings from mechanical resonance that could be misinterpreted. Attempts to overcome these problems have been attempted. For example, catheter tip pressure transducers, such as disclosed in U.S. Pat. No. 4,274,423 have employed rectangular cantilever beam type pressure sensitive diaphragms and strain gauges which were sufficiently miniaturized to measure vessel blood pressure radially of the catheter tip. Such devices have utility but are, however, subject to distortions in the pressure readings due to the resiliency of the blood vessel walls adjacent the transducer location, and their design limits their use to catheters without a balloon.
Other devices, such as shown in U.S. Pat. No. 3,550,583 represented attempts to overcome the drawbacks of the previous design for measurement of blood pressure without the use of external hydraulic connectors. The described transducer assembly had limited utility as it was incorporated into an injection needle shape which was not adapted for use in a balloon catheter structure.
In Summary therefore, for pressure recordings, the most widely used systems are fluid-filled catheters and conventional strain-gauge transducer catheters. It is well known that optimal damping of the fluid filled system and adequate frequency response of the transducer are important in obtaining accurate pressure readings. In addition, compliance of the catheter, the length and radius of the catheter, the construction of the pressure transducer, and the materials of construction, and the density and viscosity of the containing fluid are factors determining the frequency response. In particular, air bubbles in the long compliant tubing or stopcock reduce the frequency response. The combination underdamped system and a system that has a low natural frequency results in marked augmentation of the low-frequency components of pressure waves and a distorted wave form and overshoot. Since the fluid column is eliminated in the transducer catheter, the frequency response of the internal and external transducer catheters are superior to that of the fluid filled catheter system.
In conventional transducer systems, the position of the transducer is another important determinant in pressure recordings. If the reference position of the transducer is higher than the position of the chamber from which the pressure is to be recorded, the pressure reading will be lower than actual. Conversely, lowering the transducer artifactually elevates the pressure reading. This problem is eliminated by the internal transducer catheter.
A disposable transducer system has several advantages over the conventional strain gauge transducer. A disposable system is easier to handle and maintain, since the set-up for fluid infusion, long tubing, and potential of air bubbles are eliminated. Furthermore, because the disposable transducer measures the pressures within the desired chamber, careful positioning to obtain a reference point, as with conventional transducers, is not required. Also, the disposable transducer catheter allows the patient's position to be changed while the pressure is monitored and may be useful for ambulatory monitoring of pulmonary arterial pressure. Because of its high frequency response and optimal damping characteristics, it could be useful for measuring the first derivative of right ventricular pressure in the catheterization laboratory.
It has been determined also, that calibration of disposable transducer catheters has posed a serious problem. The materials of construction and the mounting of the strain gauge are sometimes critical to obtaining reproducible base line readings. It is therefore of great importance that the catheter be able to be calibrated to a reproducible base line in use in order to have more confidence in the readings obtained.
It is therefore an object of the present invention to provide a balloon catheter with a axially oriented disposable pressure transducer which in use can provide accurate, nearly instantaneous, reproducible readings of capillary pressure or pulmonary artery occluded pressure during pulmonary artery catheterization and which can also provide accurate, reproducible pressure measurements anywhere in the right side of the heart that can be reached with the catheter.